Problem: in 5.0 'check table for upgrade' doesn't detect
incompatible collation changes made in 5.0.48.

Fix: backport #39585 fix to 5.0


sql/handler.cc:
  Fix for bug#40984: backport fix from 39585 into 5.0
    - backport of #39585 fix
sql/handler.h:
  Fix for bug#40984: backport fix from 39585 into 5.0
    - backport of #39585 fix